180 u deg. to 0 u deg. phase shifter



Feb. 15, 1955 A HYMAN 2,702,365

180 TO 0 PHASE SHIFTER Filed Aug. 25. 1950 BALANCED O/RGU/T INVENTOR ABRAHAM HYMAN ATTORNEY United States Patent 180 T0 0 PHASE SHII' TER Abraham Hyman, New York, N. Y.

Application August 25, 1950, Serial No. 181,537

3 Claims. (Cl. 323-123) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of the act of April 30, 1928 (ch. 460, 45 Stat. L. 467).

This invention relates to alternating current systems, and more particularly to phase shifting devices.

It often occurs that radio engineers and others dealing with alternating current have occasion to shift the phase of a signal with which they are dealing, and it is often important that the impedance looking into the output of the phase shifter should be constant.

It is, therefore, an object of this invention to provide a phase shifter with a constant impedance looking into the output.

It is a further object of this invention to provide a simple and inexpensive phase shifter capable of 0 to 180 degrees of shift.

These objects have been accomplished in this invention which comprises a four element, four terminal bridge with two variable resistors in two opposite sides and a capacitor and an inductor in the other two opposite sides respectively, a balanced circuit load connected between two opposite terminals of said bridge, and means for supplying to the other two opposite terminals of said bridge a balanced input signal.

The invention can be clearly understood by referring to the following description and accompanying drawing wherein:

Figure l is a circuit diagram of a preferred embodiment of the invention.

Figure 2 is a diagram of a balanced circuit well known in the art, which can be used in place of the input and output transformers used in the embodiment shown in Figure 1.

In a preferred embodiment illustrated in Figure 1, the input signal is connected to the primary 1 of an input transformer 2. The secondary 3 of the input transformer has a center tap 4, which is grounded at 5. The two terminals of the secondary 3 of the input transformer are connected by lines 6 and 7 respectively to two terminals 8 and 9 of a four element, four terminal bridge. Between terminals 8 and 9 on one side of the bridge there is connected in series a first variable resistor 10, a connecting terminal 11, and an inductor 12. Between terminals 8 and 9 on the other side of the bridge there is connected in series a capacitor 13, a connecting terminal 14, and a second variable resistor 15. The two variable resistors 10 and are interconnected so that they vary inverselyone is at a maximum when the other is at a minimum and vice versa. Terminals 8 and 9 of the bridge, which are diametrically opposite each other, are seen to be the input terminals of the bridge. There is connected between terminals 11 and 14, also diametrically opposite each other, the primary 15 of an output transformer 16. The primary 15 has a center tap 17 which is grounded at 18. The two terminals of the secondary 19 of the output transformer 16 are the output terminals of the device.

Operation Consider the device as two parallel circuits, capacitor 13 and resistor 15 in one leg, and resistor 10 and inductance 12 in the other. When resistor 10 is at its maximum value (and consequently resistor 15 is at its minimum), very little current flows in the resistor 10-inductor 12 leg, but a large value of leading current flows in the capacitor 13-resistor 15 leg. This leading current finds 2,702,365 Patented Feb. 15, 1955 'ice its return path through the center tap 17 of the load transformer 16 and the ground 18. A voltage is developed across the primary 15 which in turn induces a voltage in the secondary 19. When resistor 15 is at a maximum (and consequently resistor 10 is at a minimum), very little current flows through the capacitor leg while a large lagging current will flow through the resistor 10-inductor 12 leg. The center tap 17 and ground 18 again provide the return path for this current which is now lagging, and the secondary 19 now has a voltage induced in it by a lagging current.

It is apparent that if the minimum values of the resistors 10 and 15 approach zero, then the leading current will lead degrees and the lagging current will lag 90 degrees, thus effecting a range of a full degrees of phase shift. Intermediate phase shifts can be obtained by intermediate positions of the variable resistors 10 and 15.

The impedance looking into the output terminals of the secondary 19 is:

Since R10 and R15 vary inversely, this impedance remains constant for all values of R10 and R15. In other words the sum of R10 and R15 is a constant. This is a decided advantage over the prior art.

The angle of phase shift is:

The preferred embodiment illustrated in Figure l is constituted with a center-tapped transformer as the means for supplying a balanced input signal and a second such transformer as the means for tapping a balanced output signal. This can be accomplished, either at the input or output of the bridge, by other circuits known to the art, such as the balanced network illustrated in Figure 2. The elements may be either all resistors, or may include inductance and/ or capacitor elements according to the nature of the impedances to be matched.

It is obvious that many modifications may be made in the particular embodiment described herein without departure from the scope of the invention. It is understood, therefore, that the above description is to be construed as illustrative only and is not to be construed in any limiting sense.

What is claimed is:

1. A phase shifting device comprising an input transformer with first and second secondary terminals and with a center tap in the secondary grounded; a first variable resistor with its first terminal connected to the first terminal of the input transformer secondary; a capacitor with its first terminal connected to the first terminal of the input transformer secondary; a second variable resistor with its first terminal connected to the second terminal of the input transformer secondary; an inductance with its first terminal connected to the second terminal of the input transformer secondary; an output transformer with first and second primary terminals and with a grounded primary center tap; the first primary terminal of said output transformer being connected to the second terminals of the inductance and the first variable resistor respectively; the second primary terminal of the said output transformer being connected to the second terminals of the capacitor and the second variable resistor respectively; and the two variable resistors being interconnected so that as the effective value of one is increased that of the other is decreased and the sum of their effective values is kept constant.

2. A phase shifting device comprising a four element four terminal bridge with two variable resistors one in each of two opposite sides and a capacitor and an inductor respectively in the other two opposite sides; means for inversely varying the effective values of the two variable resistors while keeping the sum of said effective values constant; a load transformer connected between two opposite terminals of said bridge with the primary of such load transformer grounded at its center; and means for supplying to the other two opposite terminals of said bridge a balanced input signal.

3. A phase shifting device comprising a four element four terminal bridge with two variable resistors one in each of two opposite sides and a capacitor and an inductor respectively in the other two opposite sides; means for inversely varying the effective values of the two variable resistors while keeping the sum of said effective values constant; means for feeding to two opposite terminals of said bridge a balanced input signal; and means for taking a balanced output signal from the other two opposite terminals of said bridge.

References Cited in the file of this patent UNITED STATES PATENTS 1,717,400 Nyquist June 18, 1929 2,042,234 Lyle May 26, 1936 2,411,423 Guptill Nov. 19, 1946 2,469,188 Werner May 3, 1949 2,559,158 Hornfeck July 3, 1951 OTHER REFERENCES Publication, A Continuously Variable Phase Shifting Device, by O. O. Pulley, The Wireless Engineer, November 1936, pp. 593 and 594. 

